One of the most popular automatic rifle designs to date, the M16 began life
as the AR15 (Armalite Rifle) at the Armalite Division of the Fairchild Aircraft
Corporation, designed by Eugene Stoner, Robert Fremont and James Sullivan.

The AR15 / M16 is actually the product of a scaled-down redesign of another
Armalite rifle, the AR-10, a rifle designed during the mid-1950s to fire the
full-power 7.62x51mm NATO cartridge. At the time, the AR-10 was unique in that
was partially constructed of lightweight materials such as aluminum forgings
and synthetic materials, which reduced weight substantially.

The USAF-sponsored "Project SALVO" opened the doors for a lightweight
rifle of .22 caliber and low recoil, designed to increase the effectiveness
of automatic fire. The AR-10 was then scaled down to accept a new cartridge,
tentatively titled the .222 Special, and eventually sold commercially as the
.223 Remington. The cartridge was classified as the 5.56x45mm M193 by the military.
Resistance to this small-caliber concept from certain military elements and
government entities led Armalite to sell rights to the AR-10 / AR15 design to
Colt's Patent Firearms Manufacturing Company in 1959.

Colt aggressively marketed the AR15 to militaries (as well as commercially),
winning sizable US contracts which found the rifles type-classified as the M16
by the US Army. The rifles were then shipped to a small but growing conflict
in Vietnam. During the Vietnam War, problems arose with the M16. Congressional
inquiry into the matter found that the problems were due in large part to Army
mismanagement (lack of training, incomplete testing of components prior to issue).
With the addition of a slightly heavier barrel, a new flash suppressor, and
a forward bolt assist, the rifle was officially adopted by the US Army in 1967
as the M16A1. Problems with the rifle quickly dissolved. Also during this time,
an experimental, shortened version of the rifle, called the CAR-15, was put
to use by special forces elements, nick-named the "commando". Slight
revisions landed it a type classification of XM177.

During the late part of the Vietnam War and into the late 1970s, NATO countries
saw which way the wind was blowing and put some effort into developing other
rifles and cartridges to improve the effectiveness of the 5.56x45mm cartridge.
Fabrique Nationale developed a new bullet for the cartridge, designated internally
as the SS109. This bullet led to the acceptance of the 5.56x45mm cartridge by
NATO. The M16 was redesigned once again to maximize reliability for the new
NATO cartridge (US M855), along with some improvements to the rifle, namely
a heavier barrel, a new flash suppressor/compensator, and a new dual-aperture
adjustable rear sight that represents a vast improvement over previous versions.
The rifle was also restricted to three-round bursts instead of full-automatic
fire in the interest of ammunition conservation. The rifle was officially type-classified
as the M16A2 in 1982.

Several military elements had expressed interest in a version of the M16A2
for urban combat, somewhere in size between the M16A2 and the XM177 Commando.
Colt developed the M4 Carbine, with a 14.5" (368mm) barrel, step-cut to
accept the M203 grenade launcher. By 1994, the M4, along with a full-automatic
version of the M16A2 that included an integrated M1913 Picatinny Rail optics-mounting
platform (M16A3), were also type-classified. Colt also shortened the M4 barrel
another three inches and now markets the resulting carbine as the M4 Commando,
a progression of the original XM177.

Development progressed with the M16 series rifles in the form of the SOPMOD
(Special Operations Peculiar Modifications) program from the Naval Surface Warfare
Center in Crane, Indiana. This program involves the addition of several aftermarket
available parts and accessories for the M4A1 Carbine, maximizing effectiveness
for special operations. This includes two sub-categories of the rifle, including
the Special Purpose Rifle (SPR), an urban sniper platform, and the Close Quarters
Battle Receiver (CQBR), yet another progression of the "commando"
carbine.

There are now countless variations of the AR15 / M16 design, manufactured and
sold by literally dozens of companies including Armalite, Bushmaster, Colt,
Diemaco, DPMS, Fabrique Nationale, Les Baer Custom, Olympic Arms, Rock River
Arms, Wilson Combat, and countless assembly companies. The M16 rifle is supported
by a vast industry providing aftermarket parts, optics, and other accessories.
This massive level of support suggests that the AR15 / M16 rifle is here for
the forseeable future.